For the light source of a projection display device, a discharge lamp such as a high-pressure mercury lamp, a metal halide lamp, or a xenon lamp is used. Such a discharge lamp emits light by arc discharge generated in a light-emitting tube. The light-emitting tube includes a roughly spherical light-emitting unit (valve), a pair of rod-shaped sealing units, and a pair of opposing electrodes. The rear ends of the electrodes are held by the sealing units, and leading ends are arranged in the valve. Further, in the sealing units, foil conductive members connected to the rear ends of the electrodes are included.
When an arc discharge occurs between the pair of electrodes, an arc (electric arc) extends in a direction opposite the direction of gravity. Accordingly, the temperature of the gravity-direction upper portion of the valve is higher than that of the same-direction lower portion of the valve. Thus, even when the upper portion and the lower portion of the valve are uniformly cooled, the temperature of the entire valve cannot be maintained uniform. However, to maintain an appropriate light-emitting state, it is important to maintain the temperature of the entire valve as uniform as possible. This is because when the temperature of the valve is higher than a predetermined temperature, clouding occurs to shorten the life of the discharge lamp. On the other hand, when the temperature of the valve is lower than the predetermined temperature, luminance reduction, flickering, or blackening occurs. The life of the discharge lamp is shortened when the blackening occurs. Further, when the temperature of a contact portion between the sealing unit and the conductive member is higher than an optimum temperature, oxidation of the conductive member is expedited, causing rupture of the light-emitting tube or a lighting failure.
The projection display device is installed in various postures in various places. For example, the projection display device may be installed on a floor or a table (first installation state). The projection display device may be suspended from a ceiling (second installation state). In the first installation state, the projection display device may be installed not only parallel to the floor but also vertical to the floor, or inclined.
In the second installation state, the projection display device may be suspended not only parallel to the ceiling but also vertical to the ceiling, or inclined with respect to the ceiling.
When the posture of the projection display device changes as described above, the posture of the light source (discharge lamp) included in the device also changes. The changed posture of the discharge lamp causes changing of the positions of the high-temperature portion and the low-temperature portion on the discharge lamp (valve). For example, the positions of the high-temperature portion and the low-temperature portion on the valve are different by 180° between when the projection display device is installed parallel to the floor and when it is suspended parallel to the ceiling. The positions of the high-temperature portion and the low-temperature portion on the valve are different by 90° between when the projection display device is installed parallel to the floor and when it is installed vertical to the floor. Thus, the temperature of the entire valve cannot be maintained uniform even when only one specific place on the valve is cooled.
Patent Literature 1 describes a light source device that includes a first duct for supplying cooling air to the gravity-direction upper portion of the valve when the projection display device is in the first installation state, and a second duct for supplying the cooling air to the gravity-direction upper portion of the valve when the projection display device is in the second installation state. In this light source device, at the inlets of the first duct and the second duct facing a fan, shielding members are arranged to reciprocate under their own weights. When the projection display device is in the first installation state, the inlet of the first duct is opened, while the inlet of the second duct is closed by the shielding member. On the other hand, when the projection display device is in the second installation state, the inlet of the second duct is opened, while the inlet of the first duct is closed by the shielding member.
Patent Literature 2 describes a light source device configured such that cooling air circulates inside a reflector surrounding a light-emitting tube.